The CTE of graphite is typically 1-4×10⁻⁶/℃, which is much lower than that of metals (such as stainless steel at 17×10⁻⁶/℃) and most ceramic materials. This characteristic plays a decisive role in core processes such as high-temperature graphitization (2800-3000℃) and carbonization of negative electrode materials.
1. Dimensional stability: Ensuring furnace loading accuracy and material bearing safety
High-temperature deformation control: The low CTE of graphite causes the graphite box to have minimal size changes at temperatures above 2800℃ (each meter of length changes by only 0.28-1.2mm), avoiding:
Interlayer misalignment and furnace jamming when the crucibles are stacked, ensuring the stable operation of continuous pusher furnaces / tunnel furnaces
Changes in the gap between the crucibles and the crucible walls, preventing material drop or disturbance of the internal airflow in the furnace
Flow channel blockage and seal failure, ensuring the uniformity of the furnace atmosphere
Maintaining mold accuracy: For custom graphite boxes with grid / layer structures, the low expansion coefficient can maintain precise internal dimensions over the long term, ensuring consistent filling volume of each batch of negative electrode materials and avoiding uneven distribution of materials due to container deformation.
2. Thermal shock resistance: Determining cycle life and production continuity
Thermal stress inhibition mechanism: The low CTE of graphite significantly reduces thermal stress (σ = E・α・ΔT/(1 - ν)), in kiln furnaces with rapid temperature changes (such as graphitization furnaces with a heating rate of up to 50℃/min):
Preventing the crucible from developing internal cracks, chipping, or fragmentation due to thermal expansion and contraction, with a damage rate much lower than that of ceramic / corundum crucibles
Capable of withstanding ≥1000 cold-hot cycles, extending the service life to 1-2 years, reducing the frequency of shutdown and replacement
Improving production stability: The graphite box with strong thermal shock resistance can be adapted to more aggressive temperature rise curves, shortening the production cycle per batch, and reducing the risk of material contamination due to crucible damage (no fragments mixed into the negative electrode powder).
3. Temperature field uniformity: Directly affecting the microstructure and electrochemical performance of negative electrode materials
Heat transfer consistency guarantee: The low expansion coefficient enables the graphite box to maintain structural integrity at high temperatures, fully exerting its excellent thermal conductivity (120-200W/m・K), ensuring:
Uniform temperature of each layer and each area of the crucible (temperature difference ≤ 5℃), avoiding insufficient or excessive graphitization degree in certain areas
Uniform crystal structure and consistent interlayer spacing of the negative electrode material, improving the first charge-discharge efficiency (first efficiency) and cycle stability
Reducing side reactions caused by temperature inhomogeneity (such as residual amorphous carbon, formation of impurity phases)
Batch consistency: After long-term use, the size change is small, ensuring that materials in different batches in the same furnace obtain the same thermal history, improving product batch consistency (such as capacity deviation ≤ 2%).
4. Material contact and separation: Affecting product purity and production efficiency
Enhanced non-stick property: The low expansion coefficient causes the surface of the graphite box to deform minimally during cold and hot cycles, maintaining a dense structure and self-lubrication, avoiding:
Negative electrode graphite powder adhering to the wall, with a discharge residual rate of ≤ 0.1%, reducing raw material waste
Material agglomeration and clustering, ensuring consistent loose bulk density
Reduced cleaning difficulty and lower labor maintenance costs
Purity control: No deformation or cracking means no detachment of graphite particles, avoiding the introduction of metal / non-metal impurities (graphite purity ≥ 99.99%), ensuring the low impurity requirements of negative electrode materials (ash content ≤ 0.3%).
5. Comprehensive cost and capacity: Key factors for long-term economic benefits
| Impact dimension | Advantages of low CTE graphite boxe | Disadvantages of high CTE materials |
|---|---|---|
| Service life | Can be recycled for ≥1000 times, with a replacement cycle of 1 to 2 years | Service life ≤ 300 times, frequent replacement |
| Load quantity | Can be stacked in multiple layers (5 to 8 layers), increasing the loading capacity by 30% | Stacking layers ≤ 3, low space utilization |
| Yield rate | Product qualification rate ≥ 99.5%, reducing rework | Pass rate ≤ 95%, scrapped due to uneven temperature / contamination |
| Energy consumption | The heating curve is more efficient, and the energy consumption per batch is reduced by 15% | Slow heating required, high energy consumption and long cycle |
